Support surfaces are used for patients that are susceptible to wounds caused by continuous pressure on any part of the body. When a patient utilizes a support surface made of materials such as air, foam, or gel, there is a likelihood of “bottoming out.” On an air or pneumatic support surface, bottoming out occurs when the air cells in a given zone, or individual cells, contain insufficient pressure to support the weight that is on them. This results in the patient coming in direct contact with the subsurface beneath the air cells. The subsurface could be a foam substrate or even the bed frame itself. Such direct contact compromises the provided pressure relief and allows high and continuous pressure points on the patient's skin, which can lead to skin breakdown.
On a foam support surface, the patient bottoms out when either (1) the patient is too heavy for the particular design of that foam mattress, i.e., the density and ILD (Indentation Load Deflection—which is a measure of the load-bearing capacity of foam) of the foam itself is not sufficient to fully support the patient without bottoming out, or (2) due to the age of the surface, the foam has lost its ability to provide proper support.
When caring for bedridden patients on a pneumatic support surface, one of the caregiver's important duties is to ensure that the patient is not “bottoming out.” To ensure this, the mattress pressures must be set to accommodate the patient in a variety of positions. This often results in cell pressures that are set higher than what is required to support the patient and to provide optimal therapy.
Surfaces used on wheelchairs, medical chairs and full mattresses often use battery power to operate the inflatable air cells. Batteries are used instead of common 120 volt line current to provide mobility, in the case of a wheelchair and patient transfers, and for remote locations, where no wall socket is conveniently available.
Battery power for the support surface needs to be of sufficient capacity to allow significant run-time between recharging cycles. This can be accomplished by using very large batteries, such as car batteries. But, of course, that has the drawback of requiring excessive size and weight. Battery chemistry (e.g., sealed lead acid, nickel metal hydride, lithium ion) can affect the battery life as well as the charging routine. However, the run-time between recharging cycles is most affected by the current draw used while the system is operating.
In practice, such systems are often left on after the patient has left the surface, which causes needless battery drain and shortens the run-time. This also results in additional recharging cycles, which shortens the battery life. This is a particular problem in the case of semi-ambulatory patients who enter and leave the surface unattended, but still need a support surface to prevent breakdown.